The present invention relates to an evaporator with a cool storage function.
For example, in order to protect the environment and improve fuel consumption of automobiles, there has been proposed an automobile designed to automatically stop the engine when the automobile stops, for example, to wait for a traffic light to change.
However, an ordinary car air conditioner has a problem in that, when an engine of an automobile in which the air conditioner is mounted is stopped, a compressor driven by the engine is stopped, and supply of refrigerant (medium for conveying cool) to an evaporator stops, whereby the cooling capacity of the air conditioner drops sharply.
As one measure to solve such a problem, imparting a cool storage function to the evaporator has been considered, to thereby enable cooling of a vehicle compartment by releasing the cool stored in the evaporator, when the compressor stops as a result of stoppage of the engine.
Such an evaporator with a cool storage function is known (see Japanese Patent Application Laid-Open (kokai) No. 2011-12947). The known evaporator includes a plurality of tube pairs each of which is composed of two flat refrigerant flow tubes and which are disposed in a heat exchange core section of the evaporator such that they are spaced from one another in the thickness direction of the refrigerant flow tubes. The two flat refrigerant flow tubes of each pair are disposed such that their longitudinal direction coincides with the vertical direction, their width direction coincides with an air-passing direction, and they are spaced from each other in the air-passing direction. Each of clearances is formed between adjacent tube pairs. One cool storage material container charged with a cool storage material is disposed in each of a plurality of clearances which are a portion of all the clearances, and is brazed to the corresponding refrigerant flow tubes. One fin is disposed in each of the remaining clearances, and is brazed to the corresponding refrigerant flow tubes. The fin is disposed in at least one of the clearances on the opposite sides of the clearance in which the cool storage material container is disposed. The entirety of the cool storage material container is located within the range of the heat exchange core section in the air-passing direction. A cool storage material containing portion whose width in the air-passing direction is constant over the entire height of the cool storage material container is provided in the cool storage material container. A cool storage material is charged into the cool storage material containing portion.
In general, a paraffin-based latent heat storage material (e.g., pentadecane, tetradecane, or the like) whose freezing point is adjusted to about 5° C. to 10° C. is used as a cool storage material which is charged into cool storage material containers of such an evaporator with a cool storage function. For example, in the evaporator with a cool storage function disclosed in Japanese Patent No. 4043776, tetradecane whose melting point is 6° C. is used as a cool storage material which is charged into cool storage material containers.
However, within the range of temperature of an environment in which the evaporator is used (e.g., within a range of −40° C. to 90° C.), the density of the cool storage material in liquid phase changes and air remaining in each cool storage material container thermally expands. As a result, the cool storage material container may break due to the internal pressure, depending on the cool storage material charging ratio, which is the ratio of the volume of the charged cool storage material to the internal volume of one closed space in the cool storage material container. Accordingly, from the viewpoint of safety, the cool storage material charging ratio must be decreased.
Incidentally, in the evaporator with a cool storage function disclosed in Japanese Patent Application Laid-Open (kokai) No. 2011-12947, the entirety of each cool storage material container is located within the range of the heat exchange core section in the air-passing direction, the cool storage material containing portion whose width in the air-passing direction is constant over the entire height of the cool storage material container is provided in the cool storage material container, and the cool storage material is charged into the cool storage material containing portion. Therefore, in the case where the above-mentioned cool storage material charging ratio is set to a low value, the level of the cool storage material in liquid phase must be relatively low, and the following problem occurs. Namely, when the evaporator with a cool storage function is incorporated into an air conditioner for a vehicle together with a compressor and a condenser, in general, the evaporator is disposed in a vertical attitude in a casing such that the heat exchange core section is located in an air passage. Therefore, the cool storage material is not present in a relatively large portion of the cool storage material container on the upper side thereof. As a result, the upper portion of the cool storage material container cannot accumulate cool, which causes a problem in that, when the compressor stops, the temperature of air flowing through a portion of the heat exchange core section, which portion corresponds to the upper portions of the cool storage material containers where the cool storage material is not present, increases more quickly than the temperature of air flowing through the remaining portion of the heat exchange core section, which portion corresponds to the remaining portions of the cool storage material containers where the cool storage material is present, and blown air temperature, which is the temperature of air passing through the evaporator with a cool storage function varies greatly.